2,674 research outputs found
Time Reversal and Exceptional Points
Eigenvectors of decaying quantum systems are studied at exceptional points of
the Hamiltonian. Special attention is paid to the properties of the system
under time reversal symmetry breaking. At the exceptional point the chiral
character of the system -- found for time reversal symmetry -- generically
persists. It is, however, no longer circular but rather elliptic.Comment: submitted for publicatio
The Chirality of Exceptional Points
Exceptional points are singularities of the spectrum and wave functions which
occur in connection with level repulsion. They are accessible in experiments
using dissipative systems. It is shown that the wave function at an exceptional
point is one specific superposition of two wave functions which are themselves
specified by the exceptional point. The phase relation of this superposition
brings about a chirality which should be detectable in an experiment.Comment: four pages, one postscript figure, to be submitted to PR
The Professionalization of the American Army through the War of 1812
The American military tradition stretches back to the militia of England. The English colonists brought a tradition of militia service and a fear of standing armies to America. Once in America, the colonies formed their own militias, using them for defense and then later for offensive operations. At the time of the American Revolution the American colonies had to combine the militia with an army. The fear of a standing army hindered the Continental Army, and then later the American Army, from being an effective force. By the time of the American Civil War, this had changed. There was a standing army as well as thousands of trained officers. When did the transformation of the American military from a citizen based ideal to a professional force occur?
Many historians point to the decades between 1820 and 1840 as the years when the army professionalized. This thesis proposes that the War of 1812 was the defining event that spurred the professionalization of the American Army. To achieve this, the American military tradition from the earliest colonists to the mid-eighteenth century is explored. This thesis divides these two hundred and fifty years into eras. Several authorsâ works are compared in each era to assess the state of the army and how it had changed from the previous era. The requirements of a professional army, the transformation of the armyâs organization, and the attitude of the American people will be analyzed in order to determine what sparked the professionalization of the American Army
Deformation of Quantum Dots in the Coulomb Blockade Regime
We extend the theory of Coulomb blockade oscillations to quantum dots which
are deformed by the confining potential. We show that shape deformations can
generate sequences of conductance resonances which carry the same internal
wavefunction. This fact may cause strong correlations of neighboring
conductance peaks. We demonstrate the relevance of our results for the
interpretation of recent experiments on semiconductor quantum dots.Comment: 4 pages, Revtex, 4 postscript figure
Chaos in Axially Symmetric Potentials with Octupole Deformation
Classical and quantum mechanical results are reported for the single particle
motion in a harmonic oscillator potential which is characterized by a
quadrupole deformation and an additional octupole deformation. The chaotic
character of the motion is srongly dependent on the quadrupole deformation in
that for a prolate deformation virtually no chaos is discernible while for the
oblate case the motion shows strong chaos when the octupole term is turned on.Comment: 6 pages LaTex plus 4 figures available by contacting the authors
directly, published in PHYS.REV.LETT. 72(1994) 235
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Structurally-related (â)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards
Accumulating data suggest that diets rich in flavanols and procyanidins are beneficial for human health. In this context, there has been a great interest in elucidating the systemic levels and metabolic profiles at which these compounds occur in humans. While recent progress has been made, there still exist considerable differences and various disagreements with regard to the mammalian metabolites of these compounds, which in turn is largely a consequence of the lack of availability of authentic standards that would allow for the directed development and validation of expedient analytical methodologies. In the present study, we developed a method for the analysis of structurally-related flavanol metabolites using a wide range of authentic standards. Applying this method in the context of a human dietary intervention study using comprehensively characterized and standardized flavanol- and procyanidin-containing cocoa, we were able to identify the structurally-related (â)-epicatechin metabolites (SREM) postprandially extant in the systemic circulation of humans. Our results demonstrate that (â)-epicatechin-3âČ-ÎČ-D-glucuronide, (â)-epicatechin-3âČ-sulfate, and a 3âČ-O-methyl(â)-epicatechin-5/7-sulfate are the predominant SREM in humans, and further confirm the relevance of the stereochemical configuration in the context of flavanol metabolism. In addition, we also identified plausible causes for the previously reported discrepancies regarding flavanol metabolism, consisting to a significant extent of inter-laboratory differences in sample preparation (enzymatic treatment and sample conditioning for HPLC analysis) and detection systems. Thus, these findings may also aid in the establishment of consensus on this topic
Orbital Magnetism in Small Quantum Dots with Closed Shells
It is found that various kind of shell structure which occurs at specific
values of the magnetic field leads to the disappearance of the orbital
magnetization for particular magic numbers of small quantum dots with an
electron number .Comment: 4 pages, latex file, four figures as postscript files, to appear at
JETP Letters, December 199
IV-VI resonant cavity enhanced photodetectors for the midinfrared
A resonant-cavity enhanced detector operating in the mid-infrared at a
wavelength around 3.6 micron is demonstrated. The device is based on a
narrow-gap lead salt heterostructure grown by molecular beam epitaxy. Below 140
K, the photovoltage clearly shows a single narrow cavity resonance, with a
relative line width of only 2 % at 80 K.Comment: 2 figure
A Simple Shell Model for Quantum Dots in a Tilted Magnetic Field
A model for quantum dots is proposed, in which the motion of a few electrons
in a three-dimensional harmonic oscillator potential under the influence of a
homogeneous magnetic field of arbitrary direction is studied. The spectrum and
the wave functions are obtained by solving the classical problem. The ground
state of the Fermi-system is obtained by minimizing the total energy with
regard to the confining frequencies. From this a dependence of the equilibrium
shape of the quantum dot on the electron number, the magnetic field parameters
and the slab thickness is found.Comment: 15 pages (Latex), 3 epsi figures, to appear in PhysRev B, 55 Nr. 20
(1997
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